1. Field of the Invention
The present invention relates to a numerical controller, and especially to a numerical controller having a machine abnormality history analysis support function.
2. Description of the Related Art
There is the technique in that, in the case where the occurrence of an abnormal load or the like on a spindle of a machine tool controlled by a numerical controller is detected, CNC information of a machine tool spindle coordinate value, an actual speed of the machine tool spindle, a tool offset set by the numerical controller in the machining, a machining program in operation or the like, is stored in a storage device of the numerical controller and utilized (for example, International Patent Application Publication No. 00/10769).
In the case where an abnormality, such as a decrease in machining accuracy for the workpiece, has occurred in the machine tool, the operator who operates the machine tool can analyze the stored CNC information to determine whether or not a problem leading to the decrease in machining accuracy, such as the spindle collision with something, occurred in the past.
If the operator is able to determine the cause of the machine abnormality, such as spindle collision, by analyzing the CNC information, the operator can further specify the cause of the spindle collision, such as an input error of the tool offset or a programming error of the machining program, by checking the tool offset, the machining program, and the like stored at the same time as the spindle collision.
According to this technique, a plurality of sets of CNC information that include not only CNC information relating to problems that occurred recently but also CNC information relating to problems that occurred during the machining of the workpiece can be stored as history records. This enables investigation of whether or not spindle collision or the like occurred, by going back to the past. It is, however, impossible to reliably determine heavy cutting or spindle collision by automatic analysis by machine. Accordingly, CNC information with a high possibility of spindle collision is automatically stored based on conditions set by each machinery manufacturer as illustrated in FIG. 7, and later the operator analyzes the stored CNC information to determine whether or not spindle collision occurred.
With this technique, however, in the case where a problem is assumed to have occurred in the machine tool, CNC information is stored even if the problem is not significant. Hence, large amounts of CNC information are stored in one numerical controller, as illustrated in FIG. 8. In order to extract CNC information about the cause of the machine abnormality, such as spindle collision, from the large amounts of CNC information, the operator needs to analyze each individual set of CNC information. Thus, there is a problem of the investigation taking long time.